Plumbing fittings are classified using the standard notation described and
illustrated below.

.

slippipe glues into

spglues into another fitting

inserttubing barb

fiptfemale threads

miptmale threads

Slip fittings are glued to pipe and may have male or female threads on one end. All are classified as "Glue and Thread." Examples: S X S, S X mipt, S X fipt, etc.
All fittings with a barbed end for flexible tubing are classified as "Insert/Barb." Insert fittings may also have a male, female or barb at the other end. Examples: I X I, I X mipt, I X fipt, etc.